Ancient Rome was a unique place. Many things we see around us today would not have been possible without the ingenuity of the Roman people. If nothing else, they were the ones who invented sanitation, made the first functional roads, and made advances in education. Oh, and wine, which is maybe even more important than anything mentioned previously. One thing that remains a huge mystery is the highly durable concrete they used for building their sturdy structures.
Fortunately, there is still hope. Scientists have recently discovered one of the possible reasons why the concrete is durable as it is. It is, as to be expected, because of the materials used to create the concrete. The main reason it seems are the volcanoes that were active at the time. As the volcanoes spewed ash, it then transformed into something known as tuff. This material was very tough and ideal for incorporating in their buildings. It was as early as 30 B.C. when Vitruvius, an engineer from that time, noticed that he could make sturdy concrete when he combined tuff, ash, lime, and seawater. What is even more interesting is the fact that this mixture created a chemical reaction that caused it to produce heat for two years after it was poured. This reaction is something called the pozzolanic reaction. In some places, a similar mixture is used even today. This is mostly down to the mixtures ability to strengthen itself and fill gaps by creating new minerals. This is all possible solely due to the chemical reaction that follows the creation of the mixture.
Unfortunately, this still does not explain why the Roman version is as durable as it is. Its durability in places where salt water is present is even more perplexing. What is even more surprising is that the material seemed to only become stronger in seawater instead of breaking down. This means that the mixture is in an open chemical exchange with the salt water that surrounds it. This is not something that is commonly used today, and it goes against most current solutions.
The thing about seawater is that it is usually much better at breaking down stuff than building it up. Water on its own can make huge canyons in the Earth’s surface. Seawater is even better at this due to the existence of minerals and salts which have even been known to eat away at boat hulls.
When examining the Roman structures, researchers found that the seawater, instead of breaking down the structure, reacted with the minerals in the ash and formed even stronger bonds.
This reaction occurs naturally during a pozzolanic reaction, but here it happened naturally during a more gradual process that went on long after the pozzolanic reaction ended.
The tobermorite that is created during this process is yet to be replicated at the low temperatures the Romans were able to do it. The tobermorite is the main reason why the Roman concrete is so durable. The cement that contains tobermorite strengthens over time, and it does so in the harshest conditions on Earth.
The consensus is that the Romans were lucky enough to have the materials required to make concrete so strong. Scientists are trying to create an analogue, but they are yet to produce anything close to what the Romans had all those years ago.